lesson.scss: 2em left padding for lists

Example of the problem: see "Ten Things You Need To Know" from http://swcarpentry.github.io/lesson-example/
For numbered lists that have more that 9 elements 1 em padding on the left is not sufficient. The result is that "1" in numbers "10" and above is printed on top of the border of encapsulating HTML block. 2 em padding solves this problem for lists with less that 100 elements. It should be safe to safe to assume that numbered lists in Carpentries' lessons should not have more than 99 items.

Starting to incorporate Library Carpentry materials

Add link to setup from schedule

Adding link to training survey to config

Adding Google Analytics code

accessibility fixes.

fix search meta tag.

Add label to search box and navigation arrows.

1. Checking that `index.md` has `root` set to '.'
2. Checking that `_config.yml` has `root` set to '..'

Fix "br" typo causing ugly rendering (epub only)

</br> instead of <br/> renders fine in the browser but not in an epub

An internally-defined Markdown link has the form [xxx][yyy].  If the
ID 'yyy' doesn't resolve, the text is left as-is, so we check for
that, then subtract those that reference configuration values using
'{{'.  It's a hack, but it'll catch at least a few things.

Import future print in case of python2 environment